1. Field of the Invention
This invention relates to a synchronous control system for synchronously controlling positions of rotation of a pair of main spindles of a machine tool including a master spindle and a slave spindle between and by which a work is to be supported for rotation at the opposite ends thereof (such a position of rotation will be hereinafter referred to only as "position").
2. Description of the Prior Art
In an apparatus of the type mentioned, working is required to position, upon preparation for operation of the apparatus, the master spindle and the slave spindle to a common target position of a same phase.
In such positioning, if the common target position is fixed to a current position of one of the main spindles, for example, the master spindle, then the slave spindle will be rotated to adjust the position thereof to the current position of the master spindle.
In this instance, if it is tried to make such positioning within a minimum angle of rotation, the slave spindle may have to be rotated reversely.
However, the two spindles including the master spindle and the slave spindle described above are connected to respective servomotors each by way of a gear box disposed on a spindle stock. Accordingly, since there is some backlash present in a gear system, there is a problem that reverse rotation of one of the main spindles has a bad influence on accuracy in positioning thereof.
On the other hand, when the slave spindle is rotated always in the forward direction to adjust the position thereof to the current position of the master spindle, the angle of rotation of the slave spindle is sometimes greater than a half cycle of rotation of the main spindles, that is, greater than 180 degrees. The angle of rotation greater than 180 degrees is not desirable for working for preparation for operation of the apparatus.